As a curable composition that includes a functional group, for example, a moisture curable liquid polymer having a crosslinkable silyl group, and involving a polysiloxane based, polyoxypropylene or polyisobutylene main chain has been hitherto known. However, the curable composition prepared using such a polymer is still to be improved in some respects. Although the polysiloxane type is superior in the weather resistance, heat resistance, cold resistance, flexibility and the like, there are still problems in staining possibility due to bleeding of the low-molecular weight component, and also to painting performance. The polyoxypropylene type is superior in the flexibility, painting performance, and stain resistance; however, to the contrary, the weather resistance may not be sufficient in some cases. Although the polyisobutylene type is characteristic in the weather resistance, and moisture-resistant permeability, it has comparatively high viscosity, and is thus disadvantageous in difficulty in handling, and also requires some ingenuity for providing in one-component type.
Furthermore, polymers having an alkenyl group as a functional group are also used as a curable composition. It is known that by using a compound having a hydrosilyl group as a curing agent, a cured product that is superior in the heat resistance, durability, and deep section curability is provided. A variety of such polymer main chain skeletons having an alkenyl group have been known, and illustrative examples include polyether polymers such as polyethylene oxide, polypropylene oxide, and polytetramethylene oxide, hydrocarbon polymers such as polybutadiene, polyisoprene, polychloroprene, and polyisobutylene or hydrogenated products thereof, polyester polymers such as polyethylene terephthalate, polybutylene terephthalate, and polycaprolactone, silicone polymers such as polydimethylsiloxane, and the like.
Also, the curable compositions prepared using any of these polymers are still to be improved in some respects. For example, the polyether cured products may have insufficient heat resistance and weather resistance in certain applications. The hydrocarbon cured products such as polybutadiene and polyisoprene may be deficient in the heat resistance and weather resistance to some extent due to the internal double bonds that remain in the main chain in certain applications. Although the polyisobutylene cured products free from internal double bonds are superior in the weather resistance, they have comparatively high viscosity, and the handling may thus be difficult. Also in the case of the polyester cured products, the weather resistance may be insufficient in certain applications. Although the silicone cured products are superior in the weather resistance, heat resistance, cold resistance, and workability, there still remain problems of paint adhesiveness, staining possibility, and the like.
On the other hand, a variety of vinyl polymers having a functional group have also been known. For example, a synthesis method of a (meth)acrylic polymer having an alkenyl group at the end in which an alkenyl group-containing disulfide is used as a chain transfer agent (see Patent Document 1 and Patent Document 2); a method for obtaining a (meth)acrylic polymer having an alkenyl group at the end which includes synthesizing a vinyl polymer having a hydroxyl group at both ends using disulfide having a hydroxyl group, followed by utilizing the reactivity of the hydroxyl group (see Patent Document 3); and a method for obtaining a (meth)acrylic polymer having a silyl group at the end which includes synthesizing a vinyl polymer having a hydroxyl group at both ends using polysulfide having a hydroxyl group, followed by utilizing the reactivity of the hydroxyl group (see Patent Document 4) were disclosed so far.
On the other hand, an acrylic rubber polymer to which an active chlorine group or an epoxy group was introduced has been used conventionally for acrylic rubber compositions for molding, whereby molded articles having superior heat resistance and oil resistance have been obtained. In this regard, in attempts to meet the needs for further improving the heat resistance, techniques for introducing a vinyl group-containing organic silicon group were proposed (see Patent Document 5 and Patent Document 6).
The curable compositions including a polymer having an alkenyl group or a crosslinkable silyl group at the side chain obtained by these methods have been utilized for paints having superior weather resistance, and the like.
However, although these methods can readily produce the polymer, to introduce a silicon group at both ends into the polymer without fail is difficult, and the cured product of the same may have insufficient rubber physical properties such as elongation. Accordingly, a curable composition having satisfactory characteristics could not be obtained. In order to introduce the functional group at both ends without fail, a chain transfer agent must be used in a large amount, thereby leading to problems in production steps. In addition, since common radical polymerization is used in these methods, to control the molecular weight, and the molecular weight distribution (ratio of weight average molecular weight and number average molecular weight) of the resulting polymer has been difficult.
Provided that the vinyl polymer having a crosslinkable silyl group at the end of the molecular chain can be produced by a simple method, cured products having superior physical properties as compared with those having a crosslinkable group at the side chain would be able to be obtained. Therefore, many researchers have investigated the production method of the same; however, their industrial production cannot be performed easily.
Accordingly, in order to solve such problems, methods for production of a (meth)acrylic polymer having a functional group at the end have been developed. In particular, in the case of polymers synthesized using living radical polymerization, the molecular weight and the molecular weight distribution can be arbitrarily controlled, and the functional group can be introduced quantitatively also to the end. As a result, such methods can be utilized in curable compositions that are superior in the weather resistance, heat resistance, oil resistance and the like, and have favorable mechanical physical properties which could not be achieved with the aforementioned polyether polymers, hydrocarbon polymers, or polyester polymers (see Patent Document 7 to Patent Document 17).
However, in the case of the vinyl polymer having at least one crosslinkable silyl group, in which the main chain is produced by a living radical polymerization process, fast curing can be hardly achieved owing to the characteristics of the functional group. Thus, photo-curing has come to be enabled by using as a functional group a vinyl polymer including a group having a polymerizable double bond such as a (meth)acryloyl group, whereby fast curing on a second time scale has come to be realized (see Patent Document 18 to Patent Document 21).
Patent Document 1: JP-A-01-247403,
Patent Document 2: JP-A-05-255415
Patent Document 3: JP-A-05-262808
Patent Document 4: JP-A-05-211922
Patent Document 5: JP-A-61-127711,
Patent Document 6: JP-B-02-001859
Patent Document 7: JP-A-09-272714,
Patent Document 8: JP-A-11-005815,
Patent Document 9: JP-A-11-043512,
Patent Document 10: JP-A-11-080571,
Patent Document 11: JP-A-11-116617,
Patent Document 12: JP-A-11-130931,
Patent Document 13: JP-A-12-086999,
Patent Document 14: JP-A-12-191912,
Patent Document 15: JP-A-2000-038404,
Patent Document 16: JP-A-2000-044626,
Patent Document 17: JP-A-2000-072804
Patent Document 18: WO 2005-030866,
Patent Document 19: JP-A-2005-105065,
Patent Document 20: JP-A-2005-023206
Patent Document 21: JP-A-2000-72816